RF coupled, implantable medical device with rechargeable back-up power source

ABSTRACT

The implantable, electrically operated medical device system comprises an implanted radio frequency (RF) receiving unit (receiver) incorporating a back-up rechargeable power supply and an implanted, electrically operated device, and an external RF transmitting unit (transmitter). RF energy is transmitted by the transmitter and is coupled into the receiver which is used to power the implanted medical device and/or recharge the back-up power supply. The back-up power supply within the receiver has enough capacity to be able to, by itself, power the implanted device coupled to the receiver for at least 24 hours during continual delivery of medical therapy. The receiver is surgically implanted within the patient and the transmitter is worn externally by the patient. The transmitter can be powered by either a rechargeable or non-rechargeable battery. In a first mode of operation, the transmitter will supply power, via RF coupled energy, to operate the receiver and simultaneously recharge the back-up power supply. In a second mode of operation, the receiver can, automatically or upon external command from the transmitter, acquire its supply of power exclusively from the back-up power supply. Yet, in a third mode of operation, the receiver can, automatically or upon command from the transmitter, alternatively acquire its supply of power from either, RF energy coupled into the receiver or the internal back-up power supply.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an implantable medical device includinga rechargeable back-up power source and a charging unit for rechargingthe back-up power source via RF coupling.

2. Description of the Related Art Including Information Disclosed Under37 CFR §§1.97-1.99

The concept of using an implantable, electrically operated medicaldevice for treating specific diseases or physical disorders is wellknown. Examples of implantable, electrically operated medical devicesare: cardiac pacemakers which restore a sick human heart to a normalrhythm, neural simulators which control nerve or brain response (such aspain or epileptic seizures), infusion pumps for subcutaneously drugdelivery (such as insulin pump), and diagnostic devices for monitoring apatient's condition.

With respect to all of these implantable, electrically operated devices,it is necessary to provide power to the device implanted below the skin.Since the medical device is subcutaneously implanted in the patient, thepower source must supply electrical energy for a reasonable period oftime in order to reduce further surgical trauma to the patient andfinancial cost to the medical provider.

Implantable, electrically operated medical devices can be classified inthree general areas: radio frequency (RF) coupled and partially poweredimplanted devices, non-rechargeable battery powered totally implanteddevices, and devices which combine RF coupling and battery poweredsystems.

The RF coupled and powered devices do not carry or contain anindependent power source. Therefore, the RF coupled device requires anexternal RF transmitter and a surgically implanted receiver. Such adevice is an RF coupled neural stimulator. The RF link transfersstimulation pulses percutaneously through the skin and adjacent tissuelayers of the patient from the external RF transmitter to the surgicallyimplanted RF receiver and stimulator device. The transmitter sends, on areal-time basis, stimulation pulses to be applied ultimately to theimplanted electrodes plus programming data defining the polarity of eachelectrode relative to each other to the implanted stimulation device.The implanted receiver obtains these stimulation pulses and programmingdata, converts pulses as necessary, delivers the energy contained ineach transmitted stimulation pulse to the implanted electrodes asdefined in the real-time programming data. The stimulation energy foreach stimulation pulse is inductively coupled on a real-time basis fromthe external transmitter to the implanted receiver.

The common disadvantage of the RF coupled and powered stimulator is thatthe patient must always wear the external transmitter and antenna (evenduring sleep) in order for the implanted receiver to deliver stimulationpulses to the targeted tissue. Stimulation therapy ceases the moment thetransmitter antenna is withdrawn just a few inches away from theimplanted receiver. Although the RF coupled stimulator has thisdisadvantage, the service life of such an RF coupled and poweredstimulator is not limited to the life of a battery contained within afully implantable stimulation unit. Accordingly, the long term cost ofthe RF coupled and powered simulators is less than the non-rechargeablebattery powered simulators because the service life of the former ismuch longer than that of the latter. RF coupled and powered simulatorshave been commercially marketed by Medtronic of Minneapolis, AveryLaboratories of New York and Neuromed of Dallas, Tex.

The battery powered stimulator utilizes a primary, non-rechargeablebattery to power the implanted stimulator. The battery provides sole andexclusive power to the implanted stimulator continually while thestimulator generates one or more electric stimulation pulses, in acontrolled manner, to the targeted tissue. Of course, the stimulationpulses are delivered to the targeted tissue via implanted leads. Anexternal programmer may be used to non-invasively adjust the stimulationparameters, such as amplitude, pulse width or rate, or to control theduration of stimulation therapy each day. Programming may be providedthrough an RF telemetry link. After programming, the stimulatorremembers the parameter values (the values are stored in an electronicmemory) as long as the battery voltage remains above a minimum voltagelevel required by the electronics. Unfortunately, the service life ofthese battery powered implantable simulators is limited to the batterylife. Accordingly, it is necessary to surgically remove and then replacethe battery powered implantable simulators upon depletion of theelectrochemically active materials in the battery. This disadvantage(i.e. surgical replacement) increases its long term cost to the medicalprovider relative to the aforementioned RF coupled and poweredsimulators. The battery powered implantable simulators do not require anexternal transmitter to deliver the stimulating electrical pulses.Accordingly, the battery powered implantable simulators are lesscomplicated to use and more comfortable to wear than the RF coupled andpowered simulators. Battery powered simulators have been marketed byMedtronic of Minneapolis and Exonix of Miami.

A third category of implantable, electrically operated devices includeneural simulators which combine the RF coupled/powered systems with thebattery powered implantable stimulator technology. These types ofsimulators enable the patient to obtain therapy without the necessity ofhaving an external RF coupled unit proximate to the implant at alltimes. However, the stimulator must be surgically replaced after thebattery is depleted if use of the external RF transmitter is notdesired. This type of stimulator allows RF coupled stimulation at timeswhen wearing the external transmitter is not objectionable, therebyextending battery life. Also, this type of stimulator may allow forcontinuing RF coupled stimulation after the internal rower source isdepleted, although some of these RF coupled and battery poweredimplantable simulators do not operate if the battery is completelydepleted in the implanted stimulator.

Several examples of such previously proposed implantable devices aredisclosed in the following U.S. patents:

U.S. Pat. No. Patentee 4,408,607 Maurer 4,793,353 Borkan 5,279,292Baumann et al. 5,314,453 Jeutter

U.S. Pat. No. 5,314,453 to Jeutter describes and claims an implant“locator” means to aid in locating an implanted device. The locatormeans comprises a reed switch affixed to the center of a transmittingcoil and a magnet affixed within the implanted device. Transmission ofhigh frequency RF energy is possible only when the reed switch is closedby the magnet within the implanted device, thus insuring some degree ofgood coupling between the transmitter and receiver. However, this patentdescribes a full wave rectifier along with rechargeable batteries.Accordingly, it incorporates a rechargeable battery. The presentinvention differs from the teachings of the Jeutter patent in thefollowing respects:

-   -   1) Charging current is controlled by battery temperature to        prevent gas generation by the battery and loss of battery        electrolyte,    -   2) A real-time feedback system is provided between the receiver        and the transmitter for real-time adjustment of the RF energy        generated by the transmitter, thereby extending the service time        of the transmitter's battery.    -   3) A low frequency RF coupling method (10 to 500,000 Hertz) is        provided which allows RF coupling through a titanium encased        receiver. The RF coupling system described by Jeutter operates        at a very high frequency of 2,000,000 Hertz which is greatly        attenuated by any metal enclosure. Jeutter describe an epoxy        potted receiver which differs from a titanium encased receiver        housing.    -   4) The receiver is capable of automatic switching the supply of        power between RF coupled power upon sensing RF energy or battery        power upon sensing loss of RF coupled power.

U.S. Pat. No. 5,279,292 to Joachim Baumann et al. teaches a seriesresonant circuit in an implantable device. The device disclosedhereinafter uses a parallel resonant circuit which can be tuned at lowfrequencies, 60 Hz to 500 kHz, such as, for example 8 kHz, which coupleswell through a titanium enclosure. Further this patent does not teachadjusting charging current as a function of battery temperature orcontrolling the charging current with the current output from a D/Aconverter.

U.S. Pat. No. 4,793,353 to William Borkan discloses a non-invasivemultiprogramable tissue stimulator which utilizes RF coupling to chargeand recharge a capacitor or other rechargeable voltage source. TheBorkan circuit differs from the circuit disclosed hereinafter in severalrespects:

-   -   1) First of al in the Borkan circuit, while in the RF        stimulation mode, each stimulation pulse must be generated and        transmitted by the transmitter, on a real time basis, to the        implanted receiver (in contrast, the receiver disclosed        hereinafter incorporates all the elements required to        autonomously generate and regulate the stimulation pulses);    -   2) Borkan teaches that a non-rechargeable battery can be used as        an alternative power source to RF coupled stimulation, while the        circuit disclosed hereinafter uses a rechargeable battery which        can be “fast” or “trickle” recharged via low to medium frequency        (10 to 500,000 Hertz) RF coupling while Borkan uses a much        higher RF coupling (2,000,000 Hertz).

U.S. Pat. No. 4,408,607 to Donald Maurer teaches a capacitive energysource and associated circuitry for powering a medical apparatus. TheMaurer circuitry differs from our the circuitry disclosed hereinafter inthat:

-   -   1) The Maurer battery is non-rechargeable and only is used to        power the implanted receiver during charging of the capacitor        (the main power source);    -   2) Maurer provides no means for non-invasively recharging the        battery;    -   3) Maurer does not control the charging current to a battery        relative to the temperature of the battery to prevent gas        generation by the battery and loss of battery electrolyte.

Moreover, Maurer does not teach the capability to switch automaticallybetween RF coupled (power upon detection of RF energy) and battery power(upon sensing absence of RF energy).

SUMMARY OF THE INVENTION

According to the present invention there is provided an implantable,electrically operated medical device comprising an implanted radiofrequency (RF) receiver incorporating a rechargeable back-up powersource and an external RF transmitter. RF transmissions are coupled intothe implanted receiver for powering delivery of medical therapy andsimultaneous recharging of the back-up power source within the receiver.The back-up power source has enough capacity to be able to autonomouslypower the receiver for at least seven days during continual delivery ofmedical therapy. The receiver is surgically implanted within the patientand the transmitter is worn externally by the patient. The transmittercan be powered by either a rechargeable or non-rechargeable battery.

In a first mode of operation, the supply of power to operate thereceiver, recharge the back-up power source and deliver therapy isacquired primarily from the RF energy coupled into the receiver, untilthe receiver senses a loss of RF power at which point it willautomatically switch to the back-up power source in order to continuedelivery of medical therapy. In this first mode of operation, thetransmitter will transmit lower energy RF waves since the back-up powersource is recharged at a slower rate.

In a second mode of operation, the receiver can, automatically or uponexternal command from the transmitter, acquire its supply of powerexclusively from the back-up power source. In the second mode ofoperation, the transmitter will transmit high energy RF waves in orderto recharge the back-up power source at a faster rate and will terminatethe RF transmission upon receiving from the receiver a “terminationcommand” which indicates that the back-up power source is fully charged.

Yet, in a third mode of operation the receiver can, automatically orupon command from the transmitter, alternatively acquire its supply ofpower from either or both, RF energy coupled into the receiver and/orthe internal back-up power source. This third mode of operation isuseful in patients where it is desirable to power the receiver from RFcoupled energy during periods of awakeness, but switch to the back-uppower source during sleep for greater comfort. In this third mode ofoperation, a real time clock within the receiver can be programmed bythe transmitter with different start/stop times for RF coupled powerthan for back-up battery power. In this fashion, the switching is doneautomatically and the external transmitter unit will alert the patientwhich is the source of power for the receiver at all times.

The receiver includes a mechanism for alerting the patient when theback-up power source is nearing depletion and needs to be recharged. Themechanism can include: 1) a vibrating device within the receiver; 2) anaudible tone generating device within the receiver; or, 3) a specificmessage shown in the transmitter's display combined with a specificaudible tone generated by the transmitter.

The transmitter incorporates a transmitting antenna which generates RFwave-fronts which are coupled into an inductor within the implantedreceiver. This RF coupled power, which is alternating current or AC innature, is rectified, filtered and converted into a high DC voltagewithin the receiver. Further, a voltage regulator within the receiverconverts the high DC voltage into a lower precise DC voltage from whichthe receiver operates.

It is the objective of the present invention to provide an implantable,electrically operated medical device (receiver) capable of obtaining itssource of electrical power from either, an external battery coupled vialow level RF transmissions (transmitter), or a back-up rechargeablebattery contained within the implanted receiver.

According to one aspect of the present invention, there is provided amethod of supplying power, on an exclusive basis, from externally lowenergy RF coupled power (transmitter), to an implanted receiver duringcontinual delivery of medical therapy.

According to another aspect of the present invention, there is providedcircuitry for programming into the receiver the times of day (meaning acontinuous 24 hour period) in which the receiver automatically switchesit's supply of power from RF coupled energy to the back-up power source,and vice-versa.

According to still another aspect of the present invention, there isprovided a method for recording into a non-volatile memory containedwithin the implanted receiver the stimulation values and other criticaldata, so that it will not be erased if the back-up power source isdepleted and to eliminate the need for the transmitter to generate andregulate, on a real time basis, the delivery of medical therapy.

According to still another aspect of the present invention, there isprovided a method of supplying power, on an exclusive basis, during atleast a seven day cycle of substantially continual delivery of medicaltherapy utilizing a rechargeable power source.

According to still another aspect of the present invention, there isprovided a method for non-invasively recharging the power source withinthe receiver, whereby the electrical energy contained in the batterypowering the external transmitter is transferred into the rechargeablepower source within the receiver utilizing an inductive RF power linkbetween the external transmitter (recharging unit) and the implantedreceiver (unit being recharged).

According to still another aspect of the present invention, there isprovided a method for regulating the rate of recharging the back-uppower source contained within the implanted receiver as a function oftemperature of the back-up power source, in order to inhibit the powersource from generating harmful gases and to prevent electrolyte loss,thereby enhancing the service life of the back-up power source andincreasing the possible number of recharge cycles.

According to still another aspect of the present invention, there isprovided a method, interactive between the transmitter and receiver, forregulating the RF energy generated by the external RF transmitter as afunction of distance between the transmitting and receiving inductors.

With these methods, the level of RF energy coupled into the receiverantenna is monitored by the receiver which telemeters specific commandsto the RF transmitter to adjust the RF energy level being generated.This real-time feedback system allows generation of just the minimum RFpower needed at the receiver, thereby extending the service time of thebattery powering the RF transmitter.

According to still another aspect of the present invention, there isprovided in transmitter for the patient to select between RF poweredoperation only, back-up power source operation only, or a combination ofboth. If “RF power” is selected, the implanted receiver will onlyoperate when the transmitter unit is proximate to the implantedreceiver, and the transmitter will generate low level RF energy. If“back-up power” is selected, the implanted receiver will draw it'soperating power exclusively from the back-up power source, and thetransmitter will generate higher level RF energy when used to quicklyrecharge the back-up power source. If “combination power” is selected,the implanted receiver will draw it's operating power from thetransmitter via low level RF coupled energy, but will automaticallyswitch to draw it's operating power from the internal back-up powersource when the transmitter is removed or turned off. The patient mayselect one of these options via a specific menu shown in thetransmitter's display.

According to still another aspect of the present invention, there isprovided a method for the receiver to automatically terminate therecharge cycle upon sensing a fully charged back-up battery by thetransmission of a specific telemetry command to the transmitter, therebyenhancing the service life of the battery powering the RF transmitter.

According to still another aspect of the present invention, there isprovided several receiver-initiated commands for alerting the patientwhen the rechargeable power source is nearing depletion and needs to berecharged. Some alerting signals are generated by the receiver itselfand other alerting signals are generated by the transmitter.

According to still another aspect of the present invention, powersources and methods are utilized for non-invasively coupling energy andrecharging the implanted battery, in combination with an implantabletissue stimulator.

According to still another aspect of the present invention, there isprovided an implantable drug delivery system utilizing these powersources and methods for non-invasively coupling electric energy into theimplanted drug delivery system and recharging its battery.

According to still another aspect of the present invention, there isprovided an implantable monitor and diagnostic system utilizing thesepower sources and methods for non-invasively coupling electrical energyinto the implanted monitor which is used to collect vital physical datafrom the patient which can be interrogated by a receiver external to thepatient.

According to still another aspect of the present invention, there isprovided an implantable cardiac pacemaker utilizing these power sourcesand methods for non-invasively coupling electrical energy into theimplanted pacemaker and recharging its battery.

According to still another aspect of the present invention, there isprovided an implantable cardioverter/defibrillator utilizing these powersources and methods for non-invasively coupling electrical energy intothe implanted cardioverter/defibrillator and recharging its battery.

According to still another aspect of the present invention, there isprovided a method for recharging power via an inductive RF power linkbetween the recharging unit and the implant and through the hermetictitanium encasement of the implant.

According to still another aspect of the present invention, a patient ispermitted to vary the delivery schedule and/or quantities of the medicaltherapy via the external RF transmitter/recharger unit.

According to still another aspect of the present invention, a medicalphysician, nurse or technician is allowed to program into the implantedmedical device, via the external RF transmitter/recharger unit, thedelivery schedule, values or quantifies of the medical therapy and toset the limit for these schedules, values or quantities within which thepatient may safely adjust them later on.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block electrical, schematic circuit diagram of the overallsystem including a transmitting unit and an implanted receiver unitconfigured for an implantable, rechargeable tissue stimulator system.

FIG. 2A is a block electrical schematic circuit of a digital to analogconverter in the receiver unit

FIG. 2B is a detailed electrical schematic circuit diagram of thedigital to analog converter with current output shown in FIG. 2A whichis used, under control of a micro controller, to regulate the constantcurrent rate for recharging the back-up power source within theimplanted receiver unit.

FIG. 3 is a block electrical schematic circuit diagram of the overallsystem as configured for an implantable, rechargeable drug deliverysystem.

FIG. 4 is a block electrical schematic circuit diagram of the overallsystem as configured for an implantable, rechargeable cardiac pacemakersystem.

FIG. 5 is a block electrical schematic circuit diagram of the overallsystem as configured for an implantable, rechargeablecardioverter/defibrillator.

FIG. 6 is a block electrical schematic circuit diagram of the overallsystem as configured for an implantable, rechargeable monitor anddiagnostic system.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring to the drawings in greater detail, there is illustrated inFIG. 1 a block electrical schematic circuit diagram of an implantable,rechargeable tissue stimulator system 10. The system 10 includes atransmitter 12 and a receiver 14, the latter being surgically implantedbeneath a patient's skin 16. The receiver 14 is connected, via leadconnector 18, to an implanted medical device, which in this embodiment,is an implanted lead 19 which contains, at it's distal end 20,stimulating electrodes 21-24. These electrodes 21-24 are implantedadjacent to the target tissue to be stimulated (i.e., a specific nerveor a nerve bundle, a specific area of the brain or a specific musclewithin the human body). The implanted receiver 14 receives therapyvalues, transmitted by the transmitter 12 via RF signals, which aredecoded by decoder 25 and then stored in a non-volatile memory (EPROM)27.

Referring again to FIG. 1, the major components of the transmitter 12are a micro controller 26 which is used, via software, to: 1) controlthe output of a programmable DC to DC converter 28 in order to regulatethe amount of RF energy to be coupled into the receiver 14; 2) read dataand command inputs inputted via a keyboard 30, display messages andmenus via a display 32, transmit therapy parameter values, via aprogramming encoder 34, a transmit drive 36 and an antenna 38, to theimplanted receiver 14; 3) and receive commands and patient's diagnosticdata, transmitted from the implanted receiver 14, via the antenna 38, anamplifier 39 and a decoder 40. Transmitter 12 has a self contained powersupply, such as a battery, whereby said transmitting unit is portableand not dependant upon an a.c. power source.

As shown in FIG. 1, when the transmitter 12 is powered up via a switch41 and a “start therapy” key 42 on the keyboard 30 is pressed, thetransmitter 12 will transmit the “start” command to the receiver 14which will initiate delivery of therapy by the receiver 14. Likewise, ifa “stop therapy” key 43 on the keyboard 30 is pressed, the transmitter12 will transmit the “stop” command to the receiver 14 which will ceasedelivery of therapy.

The implanted receiver 14 of FIG. 1 can be programmed by the physicianor patient to obtain it's operating power from one of three sources: 1)RF coupled energy only; 2) back-up rechargeable power supply/source 44only; or 3) a combination of both whereby the implanted receiver 14alternates automatically from one to the other according to a presetschedule programmed via the transmitter 12.

When “RF only” is selected from a menu displayed by the display 32 ofthe transmitter 12, an output port 45 of a micro controller 46 in thereceiver 14 is switched to a “0” and a port 47 is switched to a “1”which places pmos transistor P2 in a conducting state and pmostransistor P1 in a non-conducting state. This effectively connects aline conductor 50 to a line conductor 52, making VDD equal to the outputof a voltage regulator 54 which is at +3.0 vdc.

When “battery only” is selected from the same menu, the output port 47is switched to a “0” and the port 45 is switched to a “1”, thuseffectively connecting line conductor 56 to line conductor 52 and makingVDD equal to the voltage level at the rechargeable power source 44.

As shown in FIG. 1, when “combination” is selected from the same menu,the system 10 will automatically switch the source of VDD to the outputof the voltage regulator 54 (line conductor 50) when the transmitter 12is proximal to the receiver 14, or to the rechargeable power source 44when the transmitter 12 is removed away from the receiver 14. Theautomatic switching is performed by the micro controller 46 in responseto the state of line conductor 50 which is at +3.0 volts when RF energyis being coupled into an inductor 60 (the transmitter 12 is proximal tothe receiver 14) or is 0 volts in the absence of RF energy (thetransmitter 12 is away from the receiver 14).

When the receiver 14 is programmed to “battery only” power acquisitionmode, it's exclusive source of operating power becomes the rechargeablepower source 44. After prolonged use, the rechargeable power source 44will reach a near depleted level, at which point the receiver 14 willtransmit, via an RF communication link 61, a “recharge” command to thetransmitter 12. This will cause the transmitter 12 to generate, via thebattery 62, the DC/DC converter 28 and an output inductor 64, highenergy RF waves which are coupled into the inductor 60 contained withinthe receiver 14. The actual level of RF energy generated by the inductor64 is regulated by an output port 70 of the micro controller 26 as areal-time response to data transmitted by the receiver 14 via the microcontroller 46, the data representing the voltage level E1 at the outputof the rectifier 74 in the receiver 14 which is measured via anattenuator 76 and an analog to digital converter 78. This feedbacksystem extends the life of the battery 62 within the transmitter 12, byadjusting, as a function of distance between the inductors 64 and 60,the RF energy required to quickly recharge the rechargeable power source44. A close proximity requires much less RF energy to recharge therechargeable power source 44 than a longer distance would, in the sametime. During this recharging operation, the micro controller regulates,as a function of temperature, the current level used to recharge therechargeable power source 44. The temperature is measured by athermistor 80 which is adhered to the rechargeable power source 44during manufacturing. The junction between the thermistor 80 and aresistor 82 form a voltage divider which is fed through an analog switch84 to an analog to digital converter 86 and, via a line conductor 88, tothe micro controller 46. As the voltage rises, the ohmic value of thethermistor 80 drops proportionally to the temperature, thus reducing thevoltage at the line conductor 88 to the micro controller 46. This loopforms a temperature-controlled, current-regulated charging system whichrestricts the temperature rise of the rechargeable power source 44during recharging, thus preventing the power source 44 from sufferingelectrolyte starvation and gas generation. Both of these phenomena will,if left unchecked, dramatically reduce the reliability and service lifeof the power source 44. Also, during recharging of the power source 44,the micro controller 46 will monitor the voltage level of the powersource 44 via a line conductor 90, analog switch 92, the A/D converter86 and, finally, the line conductor 88. Upon sensing a fully chargedstate, the micro controller 46 will telemeter to transmitter 12, via theRF communications link 61, a “stop” recharging command andsimultaneously will turn off a D/A converter 94 which will cut off thecurrent needed to charge the rechargeable power source 44. In thismanner, the power source 44 cannot be overcharged, even if the “stop”command was not received by the transmitter 12 due to electromagneticinterference.

Referring to FIG. 1, when the receiver 14 is programmed to “RF only”,the power acquisition mode, it's exclusive source of operating power isthe low level RF energy generated by transmitter 12 and coupled into theinductor 60 within the receiver 14. The actual level of RF energygenerated by the inductor 64 is regulated by the output port 70 of themicro controller 26 to the minimum level required to operate thereceiver 14 and the rechargeable power source 44 is trickle charged, asa real-time response to data transmitted by the receiver 14 via themicro controller 26, i.e., the data representing the voltage level E1 atthe output of the rectifier 74 which is measured via the attenuator 76and the analog to digital converter 78. This feedback system extends thelife of the battery 62 within the transmitter 12, by adjusting the RFenergy required to operate the receiver 14 and maintain a trickle chargeto the rechargeable power source 44, as a function of the distancebetween the inductors 64 and 60. At close proximity, much less RF energyis required to accomplish these functions than at a longer distance.

During trickle charging, the micro controller 46 regulates, as afunction of temperature, the current level used to trickle charge thepower source 46, by the same method already explained in the previousparagraph. Again, this prevents electrolyte starvation and gasgeneration within the rechargeable power source 44. Also, during tricklecharging, the micro controller 46 will monitor the charge level of thepower source 44, and upon sensing a fully charged state, the receiver 14will telemeter to the transmitter 12 the “stop” recharging command andsimultaneously will turn off the D/A converter 94 which will cut off thecurrent needed to charge the power source 44. In this manner, the powersource 44 cannot be overcharged, even if the “stop” command was notreceived by the transmitter 12 due to electromagnetic interference.

When the receiver 14 is programmed to “combination” power acquisitionmode, the micro controller 46 will automatically switch delivery ofoperating power to the receiver 14 to RF coupled energy upon detectionof RF induced voltage at E1. Likewise, the micro controller 46 willswitch delivery of operating power to the rechargeable power source 44upon loss of RF induced voltage at E1. The patient may select, via amenu shown in the transmitter's display 32, fast or trickle charge tothe rechargeable power source

Upon sensing that the charge in the rechargeable power source 44 isbelow a predetermined level, the micro controller 46 signals thepatient, via an audible alarm 96 and/or a vibrating alarm 98, that therechargeable power source should be recharged.

Referring to FIG. 2B, a detailed electrical schematic of the digital toanalog (D/A) converter 94 is provided. The D/A converter 94 is softwareprogrammable, precision current source whose output is regulated by themicro controller 46. It should be noted that this type of D/A converteris best implemented into an integrated circuit where the electricalcharacteristics of the transistors can be precisely matched.

Referring again to FIG. 2B, resistor R1 is used to set the base biascurrent for the converter 94. Transistors N17 and N1 form a 1:1 currentmirror where the current into the transistor N17 equals the currentthrough the transistor N1, since both transistors have equal channelwidth and length. However, the channel width for the transistors N2through N8 are binary weighted, so that the transistor N2 has twice thewidth of the transistors N1, N3 has twice the width of N2, and so forth.This binary scaling results in transistor N2 conducting twice thecurrent of transistor N1 (assuming equal bias current), the transistorN3 conducting twice the current of the transistor N2, and so forth. Thetransistors N9 through N16 are used as pass devices to allow the currentavailable at the transistor N1 through the transistor N8 to pass to thecurrent sum line 1. The on-off state for the transistors N9 through N16is governed by inputs i1 through i8 which, in one embodiment, are outputports from the micro controller 46 (bus line 100 in FIG. 1). In thismanner, the micro controller 46 is able to select any value of currentbetween 1 and 256 times that of the current flowing through the resistorR1 (bias current) to pass to the current sum line 1.

Input line “enable.n” is used to turn on and off the D/A converter. When“enable.n” is a “0”, the transistor P1 conducts connecting VDD to thesources of the transistors P2 and P3 which form a 1:1 current mirror.Therefore, the current sourced by the transistor P3 equals the currentflowing through the transistors P2, P3 being the output current device(“iSOURCE”) for this D/A converter 94.

In FIG. 3 is shown a block diagram for an implantable, rechargeable drugdelivery system. The block diagram for the transmitter 12 is the same asfor the transmitter 12 shown in FIG. 1.

The block diagram for the receiver 14 contains the same power supplysystem, supply switching means and method for recharging therechargeable power solace 44 that has been already described above inconnection with the description of FIG. 1, but has been modified toincorporate the components required to assemble an implantable drugdelivery system. These components are: 1) a drug reservoir 104 whichcontains the drug to be delivered by the receiver 14; 2) a refill septum106 used to percutaneously, via a hypodermic needle, refill the drugreservoir 104; 3) a portioning pump 108 used to dispense a precisevolume of drug to a catheter 110 by making one or more small injections(portions); 4) a pump inlet tube 112; 5) a pump outlet tube 114; 6) thedrug delivery catheter 110 which is used to carry and deliver to thetarget tissue the drug volume dispensed by the pump 108; and 7) amulti-wire cable 118 which carries the electrical signals for drivingthe pump 108.

Referring again to FIG. 3, the wire conductors 121-123 are used to drivethe pump 108 and the wire conductors 131-133 are used to sense when aportion has been delivered. The micro controller 46 measures the timerequired for delivering each drug portion, and based on this timedetermines if the pump 108 is empty or contains fluid, since the formercondition results is a faster time than the latter. Upon sensing a “pumpempty” condition, the micro controller 46 signals the patient, via anaudible alarm 140 and/or a vibrating alarm 142, that the reservoir 104is empty. It should be noted that the titanium housing 150 of thereceiver 14 should be in close proximity to the audible alarm 140 inorder to transmit the sound waves to outside the human body.

FIG. 4 is a block diagram of an implantable, rechargeable cardiacpacemaker system. The block diagram for the transmitter 12 is the sameas for the block diagram of the transmitter 12 shown in FIG. 1.

The block diagram for the receiver 14 contains the same power supplysystem, supply switching means and method for recharging therechargeable power source 44 that already have been described above inconnection with the description of FIG. 1, but has been modified toincorporate the components required to assemble an implantable,rechargeable cardiac pacemaker system. These components are: 1) a pulseamplitude D/A converter 202 which is used to regulate, under command ofthe micro controller 46, the amplitude of the stimulating pulsesdelivered to the human heart; 2) a bus 204 which carries the binaryvalue for the amplitude from the micro controller 46 to the D/Aconverter 202; 3) an amplifier and filter 206 which detects andamplifies the cardiac depolarization waves (such as R or P waves) andfilters out other signal frequencies not related to cardiac activity; 4)an implanted lead 210 containing electrodes 211-212 which is used todeliver stimulating pulses to the heart in order to regulate the heart'srhythm, but which is used also to pick-up and carry the cardiacdepolarization waves to the amplifier/filter 206. These cardiac wavesare used by the micro controller 46 to measure the intrinsic rate of theheart. The measurement is utilized to determine if electricalstimulation pulses are needed to speed-up the heart.

Upon sensing that the charge in the rechargeable power source 44 isbelow a predetermined level, the micro controller 46 signals thepatient, via an audible alarm 220 and/or a vibrating alarm 222, that therechargeable power source 44 should be recharged.

In FIG. 5 is illustrated a block diagram of an implantable, rechargeablecardioverter/defibrillator. The block diagram for the transmitter 12 isthe same as the block diagram for the transmitter 12 shown in FIG. 1.

The block diagram for the receiver 14 contains the same power supplysystem, supply switching means and method for recharging therechargeable power source 44 that already have been described above inconnection with the description of FIG. 1, but has been modified toincorporate the components required to assemble an implantable,rechargeable cardioverter/defibrillator system. These components are: 1)a high voltage output, DC to DC converter 302 used to convert the lowvoltage available at the rechargeable power source 44 to a relativelyhigher voltage required to cardiovert a fibrillating human heart; 2) abus 304 which carries the binary value for the voltage amplitude fromthe micro controller 46 to the D/A converter 302; 3) an amplifier/filter306 used to detect the presence of a cardiac arrhythmia such asfibrillation or tachycardia; and, 4) an implanted cardioverting lead 310containing cardioverting electrodes 311-312.

As shown in FIG. 5, the DC/DC converter 302 is used to generate eitherlow voltage pulses to pace the human heart when needed or high voltagepulses to shock a large number of cardiac cells into synchrony, therebyrestoring a normal cardiac rhythm. The micro controller 46, via the bus304, regulates the timing and amplitude of low voltage pulses or highvoltage shocks, depending if an arrhythmia is detected or not. Uponsensing that the charge in the rechargeable power source 44 is below apredetermined level, the micro controller 46 signals the patient, via anaudible alarm 320 and/or a vibrating alarm 322, that the rechargeablepower source 44 should be recharged.

In FIG. 6 there is illustrated a block diagram of an implantable,rechargeable monitor and diagnostic system. The block diagram for thetransmitter 12 is the same as the block diagram for the transmitter 12shown in FIG. 1.

The block diagram for the receiver 14 contains the same power supplysystem, supply switching means and method for recharging therechargeable power source 44 that already have been described inconnection with the description of FIG. 1, but has been modified toincorporate the components required to assemble an implantable,rechargeable monitor and diagnostic system. These components are: 1) anamplifier/filter 406 used to amplify the desired biological signals andto filter out other undesirable signals; 2) an analog to digitalconverter 408 which is used to convert the biological signal into adigital value representative of frequency and amplitude of thebiological signal; 3) a monitoring lead 410 containing electrodes411-412 which are used to pick-up and carry the biological signals tothe amplifier/filter 406.

The mission of the monitor and diagnostic system shown in FIG. 6 is tomonitor and record, in a non-volatile memory 414 27, specific biologicalsignals and events occurring adjacent to the monitoring electrodes411-412. Later, at a convenient time, these recordings can betelemetered to the transmitter 12 which will produce, via a graphicrecorder 416, a hard copy of the biological signals for the physician'sexamination and eventual diagnosis. Any time biological signals occur,they are scrutinized by the micro controller 46 for specific morphologywhich would cause the event to be stored into the memory 27 for laterexamination by the physician. An example of a typical use, would be torecord dysfunctional endocardiac signals which, when inspected by atrained physician, may reveal the origin of a cardiac dysfunction notdetected by conventional means, such as a surface EKG.

From the foregoing description, it will be apparent that the RF coupled,implantable medical system 10 with the rechargeable back-up powersupply/source 44 of the present invention has a number of advantages,some of which have been described above and others of which are inherentin the invention. Also it will be understood that modifications can bemade to the RF coupled, implantable medical system including therechargeable back-up power supply/source 44 described above withoutdeparting from the teachings of the present invention. Accordingly, thescope of the invention is only to be limited as necessitated by theaccompanying claims.

1. An RF coupled implantable medical system comprising: a transmittingunit; a receiving unit including an implantable, electrically operated,medical device, RF energy receiving means, RF signal transmitting meansand a rechargeable battery; said transmitting unit including a powersource, RF energy transmitting means, RF signal receiving means andfirst control means coupled to said RF energy transmitting means and tosaid RF signal receiving means for controlling the amount of RF energytransmitted to said receiving unit thereby to conserve on the amount ofpower obtained from said power source; and, second control means coupledto said RF energy receiving means, to said rechargeable battery, to saidRF signal transmitting means and to said implantable medical device, foradjusting the charging current flowing into said rechargeable battery,as a function of (a) the charge level of said rechargeable battery, (b)selected charging rate, and (c) selected power supply for theimplantable medical device.
 2. The system of claim 1 wherein saidreceiving unit includes a titanium housing enclosing said RF energyreceiving means, said RF signal transmitting means, said rechargeablebattery and said second control means.
 3. The system of claim 1 whereinsaid RF energy transmitting means of said transmitting unit isconstructed to transmit energy at a frequency as low as 10 Hz and up toat least 20,000 Hz.
 4. The system of claim 1 wherein said rechargeablebattery has a temperature sensor which is mounted closely adjacentthereto and which is coupled via said RF signal transmitting means tosaid first control means of said transmitting unit whereby the level oftransmitted RF energy can be reduced proportionally to the reduction incharging rate of the rechargeable battery in said receiving unit, inorder to reduce the power consumption from said power source poweringsaid transmitting unit.
 5. The system of claim 1 wherein said RF energytransmitting means of said transmitting unit includes mode selectionmeans for recharging said rechargeable battery at a “fast” (highenergy), high energy rate or at a “trickle” (low to medium energy), lowto medium energy rate.
 6. The system of claim 1 wherein saidtransmitting unit includes power source selection means for setting saidreceiving unit to obtain its operating power from (1) RF coupled energy(“RF only” mode) in a “RF only” mode, (2) said rechargeable battery(“battery only” mode) in a “battery only” mode or (3) automaticallyswitch to “RF only” upon detection of said RF energy field, or “batteryonly” when said RF energy field is not detected (“combination” mode) ina “combination” mode.
 7. The system of claim 6 wherein said receivingunit includes: (a) means for rectifying said RF energy into a relativelyhigh D.C. voltage, (b) means for regulating said high D.C. voltage intoa lower D.C. voltage, and (c) means for detecting the presence of saidRF energy field, said receiving unit, when set to operate in said “RFcoupled energy” mode, is operable to supply regulated electrical energyto said implantable device so long as said transmitting unit is locatedproximate to said receiving unit and said receiving unit is sensingtransmitted RF energy.
 8. The system of claim 6 wherein said receivingunit, when said transmitting unit is set to operate in said “batteryonly” mode, is operable, periodically, to supply electrical energy tosaid implantable device from said rechargeable power supply for a periodof at least 24 hours.
 9. The system of claim 6 wherein said receivingunit, when set to operate in said “combination” mode, is operable tosupply regulated D.C. electrical energy to said implantable device, solong as said transmitting unit is located proximate to said receivingunit, and, separately, to “trickle charge” said rechargeable battery tomaintain same fully charged.
 10. The system of claim 1 wherein saidfirst control means of said transmitting unit includes means forcontrolling the level of RF energy transfer from the transmitting unitto the receiving unit relative to one or more of one or more of thefollowing parameters: (a) the charge level of said rechargeable battery,(b) selected charging rate, and (c) the selected power supply for saidreceiving unit.
 11. The system of claim 1 wherein said receiving unitcomprises means for measuring the charge level of said rechargeablebattery and, upon sensing a fully charged battery, automaticallyup-links a coded signal which commands said transmitting unit to “stop”transmitting RF energy.
 12. The system of claim 1 wherein saidtransmitting unit includes a visual display coupled to said firstcontrol means.
 13. The system of claim 1 wherein said transmitting unitincludes a keyboard coupled to said first control means.
 14. The systemof claim 13 wherein said keyboard includes keys to start and stoprecharging of said rechargeable battery within the implantable medicaldevice.
 15. The system of claim 1 wherein said implanted medical deviceis a tissue stimulator.
 16. The system of claim 1 wherein said implantedmedical device is a drug delivery system.
 17. The system of claim 1wherein said implanted medical device is a cardiac pacemaker system. 18.The system of claim 1 wherein said implanted medical device is acardioverter/defibrillator.
 19. The system of claim 1 wherein saidtransmitting unit includes a battery, whereby said transmitting unit isportable and not dependant dependent upon an a.c. power source.
 20. Thesystem of claim 19 wherein said battery can be a rechargeable battery ora non-rechargeable battery.
 21. The system of claim 1 wherein said RFenergy transmitting means of said transmitting unit includes modeselection means for setting said transmitting unit to operate in one ofthe following modes: “RF only”, “battery only” or a “combination ofboth”.
 22. The system of claim 21 wherein said RF energy transmittingmeans of said transmitting unit controls the amount of RF energytransmitted and, (a) when said implanted receiving unit is set tooperate in said “RF only” mode, said transmitted RF energy isautomatically adjusted to the amount of RF energy required (i) tooperate said implanted device and (ii) to maintain said rechargeablebattery, which is powering said implanted device, in a fully chargedstate; (b) when said implanted receiving unit is set to operate in said“battery only” mode, said transmitted RF energy is automaticallyadjusted to the amount of RF energy required (i) to operate saidimplanted device and (ii) to recharge quickly said rechargeable batterywhich is powering said implanted device; and, (c) when said implantedreceiving unit is set to operate in said “combination of both” mode,said receiving unit is set to switch automatically to either said “RFonly” mode upon detecting said transmitted RF energy, or to said“battery only” mode upon detecting a loss of said transmitted RF energy.23. An RF coupled implantable medical system comprising: a transmittingunit; a receiving unit including an implantable, electrically operated,medical device; said transmitting unit including RF energy transmittingmeans, RF signal receiving means and first control means coupled to saidRF energy transmitting means and to said RF signal receiving means forcontrolling the amount of RF energy transmitted to said receiving unit;said receiving unit including RF energy receiving means, RF signaltransmitting means, a rechargeable power supply coupled to said RFenergy receiving means and second control means for adjusting thecharging current flowing into said rechargeable battery coupled to saidrechargeable power supply means, to said RF energy receiving means, tosaid RF signal transmitting means and to said implanted medical device,and mode selection means for setting said receiving unit to operate inone of the following modes: (1) “RF only”, (2) “battery only” or (3)“combination of both”.
 24. The system of claim 23 wherein said receivingunit, when said transmitting unit is set to operate in said “RF only”mode, is operable to supply electrical energy to said implantabledevice, so long as said transmitting unit is located proximate to saidreceiving unit and said receiving unit is sensing transmitted RF energy.25. The system of claim 23 wherein said receiving unit, when saidtransmitting unit is set to operate in said “battery only” mode, isoperable. periodically, to supply electrical energy to said implantabledevice from said rechargeable power supply for a period of at least 7days.
 26. The system of claim 23 wherein said receiving unit, when saidtransmitting unit is set to operate in said “battery only” mode, isoperable, periodically, to supply electrical energy to said implantabledevice from said rechargeable power supply for a period of at least 24hours.
 27. The system of claim 23 wherein said receiving unit, when saidtransmitting unit is set to operate in said “combination” mode, isoperable to supply electrical energy to said implantable device througha rectifier directly to said implanted medical device, so long as saidtransmitting unit is located proximate to said receiving unit, and,separately, to “trickle charge” said rechargeable power supply.
 28. AnRF coupled implantable medical system comprising: a transmitting unit; areceiving unit including an implantable, electrically operated, medicaldevice; said transmitting unit including RF energy transmitting means,RF signal receiving means and first control means coupled to said RFenergy transmitting means and to said RF signal receiving means forcontrolling the amount of RF energy transmitted to said receiving unit;said receiving unit including RF energy receiving means, RF signaltransmitting means, a rechargeable power supply coupled to said RFenergy receiving means and second control means for adjusting thecharging current flowing into said rechargeable battery coupled to saidrechargeable power supply means, the current to said RF energy receivingmeans, the current to said RF signal transmitting means and to outputsignals from an output of said implanted medical device; and, saidreceiving unit comprising means for measuring the charge level of saidrechargeable battery power supply and, upon sensing a fully chargedbattery power supply, automatically up-linking a coded signal whichcommands said transmitting unit to “stop” stop transmitting RF energy;and, mode selection means for controlling the supply of power in one ofseveral modes of operation selected from one of: a) simultaneouslyoperate the implanted medical device and recharge the rechargeable powersupply from the transmitted RF energy, b) operate the implanted medicaldevice exclusively exclusively from the rechargeable power supply, or c)operate the implanted medical device from the transmitted RF energy. 29.An RF coupled implantable medical system comprising: a transmittingunit; a receiving unit including an implantable, electrically operated,medical device, RF energy receiving means, and a rechargeable powersupply; said transmitting unit including a power source and an RF energytransmitting means; said receiving unit including control means coupledto said rechargeable power supply and to said implantable medical devicefor adjusting the charging current flowing into said rechargeable powersupply; and, mode selection means for controlling the supply of power inone of several modes of operation selected from one of: a)simultaneously operate the implanted medical device and recharge therechargeable power supply from the transmitted RF energy, b) operate theimplanted medical device exclusively from the rechargeable power supply,or c) operate the implanted medical device from the transmitted RFenergy.
 30. An RF coupled implantable medical system of claim 29 furthercomprising memory means coupled to said control means for storinginformation for controlling an output signal from said implantablemedical device.
 31. An RF coupled implantable medical system comprising:a transmitting unit; a receiving unit including an implantable,electrically operated, medical device, RF energy receiving means, and arechargeable power supply; said transmitting unit including a powersource, RF energy transmitting means, and transmitting control meanscoupled to said RF energy transmitting means for controlling the amountof RF energy transmitted to said receiving unit thereby to conserve onthe amount of power obtained from said power source; said receiving unitincluding second control means coupled to said rechargeable power supplyand to said implantable medical device for adjusting the chargingcurrent flowing into said rechargeable power supply; and, mode selectionmeans for controlling the supply of power in one of several modes ofoperation selected from one of: a) simultaneously operate the implantedmedical device and recharge the rechargeable power supply from thetransmitted RF energy, b) operate the implanted medical deviceexclusively from the rechargeable power supply, or c) operate theimplanted medical device from the transmitted RF energy.
 32. An RFcoupled implantable medical system of claim 31 further comprising memorymeans coupled to said second control means for storing information forcontrolling an output signal from said implantable medical device.